If a map of a city is encoded as a Digital Elevation Model, it becomes amenable to image-processing software, such as the public-domain NIH Image application. Standard techniques can be used to measure plan areas and volumes and simple macros can be devised to measure perimeter length and wall areas. A macro for calculating shadow volumes is elaborated for the simulation of solar gains and daylight, including indirect lighting, leading to the possibility of an image-based urban-scale environmental model.